android_system_core/libunwindstack/ElfInterface.cpp

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <elf.h>
#include <stdint.h>

#include <memory>
#include <string>

#include "DwarfDebugFrame.h"
#include "DwarfEhFrame.h"
#include "DwarfSection.h"
#include "ElfInterface.h"
#include "Log.h"
#include "Memory.h"
#include "Regs.h"
#include "Symbols.h"

ElfInterface::~ElfInterface() {
  for (auto symbol : symbols_) {
    delete symbol;
  }
}

template <typename AddressType>
void ElfInterface::InitHeadersWithTemplate() {
  if (eh_frame_offset_ != 0) {
    eh_frame_.reset(new DwarfEhFrame<AddressType>(memory_));
    if (!eh_frame_->Init(eh_frame_offset_, eh_frame_size_)) {
      eh_frame_.reset(nullptr);
      eh_frame_offset_ = 0;
      eh_frame_size_ = static_cast<uint64_t>(-1);
    }
  }

  if (debug_frame_offset_ != 0) {
    debug_frame_.reset(new DwarfDebugFrame<AddressType>(memory_));
    if (!debug_frame_->Init(debug_frame_offset_, debug_frame_size_)) {
      debug_frame_.reset(nullptr);
      debug_frame_offset_ = 0;
      debug_frame_size_ = static_cast<uint64_t>(-1);
    }
  }
}

template <typename EhdrType, typename PhdrType, typename ShdrType>
bool ElfInterface::ReadAllHeaders() {
  EhdrType ehdr;
  if (!memory_->Read(0, &ehdr, sizeof(ehdr))) {
    return false;
  }

  if (!ReadProgramHeaders<EhdrType, PhdrType>(ehdr)) {
    return false;
  }

  // We could still potentially unwind without the section header
  // information, so ignore any errors.
  if (!ReadSectionHeaders<EhdrType, ShdrType>(ehdr)) {
    log(0, "Malformed section header found, ignoring...");
  }
  return true;
}

template <typename EhdrType, typename PhdrType>
bool ElfInterface::ReadProgramHeaders(const EhdrType& ehdr) {
  uint64_t offset = ehdr.e_phoff;
  for (size_t i = 0; i < ehdr.e_phnum; i++, offset += ehdr.e_phentsize) {
    PhdrType phdr;
    if (!memory_->ReadField(offset, &phdr, &phdr.p_type, sizeof(phdr.p_type))) {
      return false;
    }

    if (HandleType(offset, phdr.p_type)) {
      continue;
    }

    switch (phdr.p_type) {
    case PT_LOAD:
    {
      // Get the flags first, if this isn't an executable header, ignore it.
      if (!memory_->ReadField(offset, &phdr, &phdr.p_flags, sizeof(phdr.p_flags))) {
        return false;
      }
      if ((phdr.p_flags & PF_X) == 0) {
        continue;
      }

      if (!memory_->ReadField(offset, &phdr, &phdr.p_vaddr, sizeof(phdr.p_vaddr))) {
        return false;
      }
      if (!memory_->ReadField(offset, &phdr, &phdr.p_offset, sizeof(phdr.p_offset))) {
        return false;
      }
      if (!memory_->ReadField(offset, &phdr, &phdr.p_memsz, sizeof(phdr.p_memsz))) {
        return false;
      }
      pt_loads_[phdr.p_offset] = LoadInfo{phdr.p_offset, phdr.p_vaddr,
                                          static_cast<size_t>(phdr.p_memsz)};
      if (phdr.p_offset == 0) {
        load_bias_ = phdr.p_vaddr;
      }
      break;
    }

    case PT_GNU_EH_FRAME:
      if (!memory_->ReadField(offset, &phdr, &phdr.p_offset, sizeof(phdr.p_offset))) {
        return false;
      }
      eh_frame_offset_ = phdr.p_offset;
      if (!memory_->ReadField(offset, &phdr, &phdr.p_memsz, sizeof(phdr.p_memsz))) {
        return false;
      }
      eh_frame_size_ = phdr.p_memsz;
      break;

    case PT_DYNAMIC:
      if (!memory_->ReadField(offset, &phdr, &phdr.p_offset, sizeof(phdr.p_offset))) {
        return false;
      }
      dynamic_offset_ = phdr.p_offset;
      if (!memory_->ReadField(offset, &phdr, &phdr.p_memsz, sizeof(phdr.p_memsz))) {
        return false;
      }
      dynamic_size_ = phdr.p_memsz;
      break;
    }
  }
  return true;
}

template <typename EhdrType, typename ShdrType>
bool ElfInterface::ReadSectionHeaders(const EhdrType& ehdr) {
  uint64_t offset = ehdr.e_shoff;
  uint64_t sec_offset = 0;
  uint64_t sec_size = 0;

  // Get the location of the section header names.
  // If something is malformed in the header table data, we aren't going
  // to terminate, we'll simply ignore this part.
  ShdrType shdr;
  if (ehdr.e_shstrndx < ehdr.e_shnum) {
    uint64_t sh_offset = offset + ehdr.e_shstrndx * ehdr.e_shentsize;
    if (memory_->ReadField(sh_offset, &shdr, &shdr.sh_offset, sizeof(shdr.sh_offset)) &&
        memory_->ReadField(sh_offset, &shdr, &shdr.sh_size, sizeof(shdr.sh_size))) {
      sec_offset = shdr.sh_offset;
      sec_size = shdr.sh_size;
    }
  }

  // Skip the first header, it's always going to be NULL.
  offset += ehdr.e_shentsize;
  for (size_t i = 1; i < ehdr.e_shnum; i++, offset += ehdr.e_shentsize) {
    if (!memory_->ReadField(offset, &shdr, &shdr.sh_type, sizeof(shdr.sh_type))) {
      return false;
    }

    if (shdr.sh_type == SHT_SYMTAB || shdr.sh_type == SHT_DYNSYM) {
      if (!memory_->Read(offset, &shdr, sizeof(shdr))) {
        return false;
      }
      // Need to go get the information about the section that contains
      // the string terminated names.
      ShdrType str_shdr;
      if (shdr.sh_link >= ehdr.e_shnum) {
        return false;
      }
      uint64_t str_offset = ehdr.e_shoff + shdr.sh_link * ehdr.e_shentsize;
      if (!memory_->ReadField(str_offset, &str_shdr, &str_shdr.sh_type, sizeof(str_shdr.sh_type))) {
        return false;
      }
      if (str_shdr.sh_type != SHT_STRTAB) {
        return false;
      }
      if (!memory_->ReadField(str_offset, &str_shdr, &str_shdr.sh_offset,
                              sizeof(str_shdr.sh_offset))) {
        return false;
      }
      if (!memory_->ReadField(str_offset, &str_shdr, &str_shdr.sh_size, sizeof(str_shdr.sh_size))) {
        return false;
      }
      symbols_.push_back(new Symbols(shdr.sh_offset, shdr.sh_size, shdr.sh_entsize,
                                     str_shdr.sh_offset, str_shdr.sh_size));
    } else if (shdr.sh_type == SHT_PROGBITS && sec_size != 0) {
      // Look for the .debug_frame and .gnu_debugdata.
      if (!memory_->ReadField(offset, &shdr, &shdr.sh_name, sizeof(shdr.sh_name))) {
        return false;
      }
      if (shdr.sh_name < sec_size) {
        std::string name;
        if (memory_->ReadString(sec_offset + shdr.sh_name, &name)) {
          uint64_t* offset_ptr = nullptr;
          uint64_t* size_ptr = nullptr;
          if (name == ".debug_frame") {
            offset_ptr = &debug_frame_offset_;
            size_ptr = &debug_frame_size_;
          } else if (name == ".gnu_debugdata") {
            offset_ptr = &gnu_debugdata_offset_;
            size_ptr = &gnu_debugdata_size_;
          }
          if (offset_ptr != nullptr &&
              memory_->ReadField(offset, &shdr, &shdr.sh_offset, sizeof(shdr.sh_offset)) &&
              memory_->ReadField(offset, &shdr, &shdr.sh_size, sizeof(shdr.sh_size))) {
            *offset_ptr = shdr.sh_offset;
            *size_ptr = shdr.sh_size;
          }
        }
      }
    }
  }
  return true;
}

template <typename DynType>
bool ElfInterface::GetSonameWithTemplate(std::string* soname) {
  if (soname_type_ == SONAME_INVALID) {
    return false;
  }
  if (soname_type_ == SONAME_VALID) {
    *soname = soname_;
    return true;
  }

  soname_type_ = SONAME_INVALID;

  uint64_t soname_offset = 0;
  uint64_t strtab_offset = 0;
  uint64_t strtab_size = 0;

  // Find the soname location from the dynamic headers section.
  DynType dyn;
  uint64_t offset = dynamic_offset_;
  uint64_t max_offset = offset + dynamic_size_;
  for (uint64_t offset = dynamic_offset_; offset < max_offset; offset += sizeof(DynType)) {
    if (!memory_->Read(offset, &dyn, sizeof(dyn))) {
      return false;
    }

    if (dyn.d_tag == DT_STRTAB) {
      strtab_offset = dyn.d_un.d_ptr;
    } else if (dyn.d_tag == DT_STRSZ) {
      strtab_size = dyn.d_un.d_val;
    } else if (dyn.d_tag == DT_SONAME) {
      soname_offset = dyn.d_un.d_val;
    } else if (dyn.d_tag == DT_NULL) {
      break;
    }
  }

  soname_offset += strtab_offset;
  if (soname_offset >= strtab_offset + strtab_size) {
    return false;
  }
  if (!memory_->ReadString(soname_offset, &soname_)) {
    return false;
  }
  soname_type_ = SONAME_VALID;
  *soname = soname_;
  return true;
}

template <typename SymType>
bool ElfInterface::GetFunctionNameWithTemplate(uint64_t addr, std::string* name,
                                               uint64_t* func_offset) {
  if (symbols_.empty()) {
    return false;
  }

  for (const auto symbol : symbols_) {
    if (symbol->GetName<SymType>(addr, load_bias_, memory_, name, func_offset)) {
      return true;
    }
  }
  return false;
}

bool ElfInterface::Step(uint64_t pc, Regs* regs, Memory* process_memory) {
  // Need to subtract off the load_bias to get the correct pc.
  if (pc < load_bias_) {
    return false;
  }
  pc -= load_bias_;

  // Try the eh_frame first.
  DwarfSection* eh_frame = eh_frame_.get();
  if (eh_frame != nullptr && eh_frame->Step(pc, regs, process_memory)) {
    return true;
  }

  // Try the debug_frame next.
  DwarfSection* debug_frame = debug_frame_.get();
  if (debug_frame != nullptr && debug_frame->Step(pc, regs, process_memory)) {
    return true;
  }

  return false;
}

// Instantiate all of the needed template functions.
template void ElfInterface::InitHeadersWithTemplate<uint32_t>();
template void ElfInterface::InitHeadersWithTemplate<uint64_t>();

template bool ElfInterface::ReadAllHeaders<Elf32_Ehdr, Elf32_Phdr, Elf32_Shdr>();
template bool ElfInterface::ReadAllHeaders<Elf64_Ehdr, Elf64_Phdr, Elf64_Shdr>();

template bool ElfInterface::ReadProgramHeaders<Elf32_Ehdr, Elf32_Phdr>(const Elf32_Ehdr&);
template bool ElfInterface::ReadProgramHeaders<Elf64_Ehdr, Elf64_Phdr>(const Elf64_Ehdr&);

template bool ElfInterface::ReadSectionHeaders<Elf32_Ehdr, Elf32_Shdr>(const Elf32_Ehdr&);
template bool ElfInterface::ReadSectionHeaders<Elf64_Ehdr, Elf64_Shdr>(const Elf64_Ehdr&);

template bool ElfInterface::GetSonameWithTemplate<Elf32_Dyn>(std::string*);
template bool ElfInterface::GetSonameWithTemplate<Elf64_Dyn>(std::string*);

template bool ElfInterface::GetFunctionNameWithTemplate<Elf32_Sym>(uint64_t, std::string*,
                                                                   uint64_t*);
template bool ElfInterface::GetFunctionNameWithTemplate<Elf64_Sym>(uint64_t, std::string*,
                                                                   uint64_t*);